1. Field of the Invention
The present invention generally relates to electronic sectionalizers and, more particularly, is concerned with a resettable internal actuating mechanism for use with an electronic sectionalizer.
2. Description of the Prior Art
High voltage power distribution systems are typically comprised of a main supply line that is connected to a number of branch or lateral lines. Normally, the main line is protected near its source of power by an automatic recloser or a reclosing circuit breaker which is operable to disable the entire system downstream of the recloser if currents above a certain magnitude are detected. Automatic reclosers and reclosing circuit breakers are particularly useful for enabling transient fault currents to clear after which time the recloser can again energize the circuit. However, if fault current conditions remain, the recloser after one or more attempts to re-energize the circuit will cease operation and cause the distribution system to remain in a deactivated state until attended by a repairman.
In the past, fuse links were often installed at the beginning of each lateral line to protect the line and isolate it from the rest of the distribution system where over-current conditions existed only in a particular lateral line. Many problems were observed, however, in attempting to coordinate the opening characteristics of the fuse links with the reclosing apparatus and in attempting to ensure that the fuse link would not melt and open the lateral line before the reclosing apparatus had an opportunity to deactivate the entire system. As a consequence, electronic sectionalizers have been developed which instead count the number of times that the recloser opens and closes the circuit. After a specified number of current flow periods or "shots," the electronic sectionalizer disables the lateral line during a subsequent dead interval when the reclosing apparatus has opened if over-current conditions in the lateral line protected by the sectionalizer are detected. For additional disclosure of electronic sectionalizers, reference is hereby made to U.S. Pat. No. 4,553,188 to Aubrey et al. and U.S. Pat. No. 4,768,010 to Brown et al.
Various actuating mechanisms have been developed in recent years having actuators for releasing sectionalizers. The typical actuator operates in conjunction with a pivot mechanism which cooperates with a latch that is released or opened by the actuating mechanism. In other words, once fired, the actuator causes a latch or release lever to swing and then a spring and/or the forces of gravity are utilized so as to complete the pivotal movement and ensure that the tube of the sectionalizer shifts downwardly and away from the upper contact to open the lateral line. Thus, the force exerted by the actuator does not directly impart movement of the tube toward an isolating position, but merely moves a latch so that either an over-centering spring or the force of gravity is subsequently operable to urge the tube to fall away from the upper contact.
Representative examples of these actuating mechanisms are disclosed in U.S. Pat. Nos. 4,768,010 and 4,795,996 to Brown et al., U.S. Pat. No. 5,162,967 to Torrontegui and U.S. Pat. No. 5,172,090 to Ranjan et al. In a first approach, the disclosure in U.S. Pat. No. 4,768,010 to Brown includes a detonation actuator which can be used only once and requires replacement after the actuator is detonated and the sectionalizer tube is released. In a second approach, a resettable solenoid-type actuator is disclosed in U.S. Pat. No. 4,795,996 to Brown and in the patents to Torrontegui and Ranjan. The actuating mechanisms in the patents which follow this second approach are either external or internal. In the patent to Ranjan, the actuator is external. A problem exists, however, with those actuators which are external in that they are exposed to environmental conditions subjecting them to corrosion and/or ice which may prevent the successful drop-out of the sectionalizer tube. Wind and stormy weather may also cause the actuating mechanism to vibrate and thus to result in the unwanted triggering of the release of the sectionalizer tube. While the actuator disclosed in U.S. Pat. No. 4,795,996 to Brown is mostly internal, the mechanism remains susceptible to vibration from wind and stormy weather. Although the actuator disclosed in the patent to Torrontegui is entirely internal, a problem remains in that the sectionalizer assembly has many parts and is unduly complex.
Consequently, a need still exists for an actuating mechanism designed to overcome the aforementioned problems in the prior art without introducing any new problems in their place.